Fix explicit UTF8Bom encoding on Windows PowerShell 5.1

Source/Private/SetModuleContent.ps1

@@ -34,6 +34,10 @@ function SetModuleContent {
     )
     begin {
         Write-Debug "SetModuleContent WorkingDirectory $WorkingDirectory"
+        # Windows PowerShell's Set-Content has no UTF8Bom encoding, but its UTF8 encoding writes a BOM
+        if (-not $IsCoreCLR -and $Encoding -eq "UTF8Bom") {
+            $Encoding = "UTF8"
+        }
         Write-Debug "Encoding $Encoding"
         Push-Location $WorkingDirectory -StackName SetModuleContent
         $ContentStarted = $false # There has been no content yet

Source/Public/ConvertTo-Script.ps1

@@ -87,6 +87,10 @@ function ConvertTo-Script {
             }
         }
 
+        # Windows PowerShell's Set-Content has no UTF8Bom encoding, but its UTF8 encoding writes a BOM
+        if (-not $IsCoreCLR -and $Encoding -eq "UTF8Bom") {
+            $Encoding = "UTF8"
+        }
         $SetContentCmd = $ExecutionContext.InvokeCommand.GetCommand('Microsoft.PowerShell.Management\Set-Content', [System.Management.Automation.CommandTypes]::Cmdlet)
         Write-Debug "    EXIT: ConvertTo-Script BEGIN"
     }

Source/Public/Invoke-ScriptGenerator.ps1

@@ -82,6 +82,10 @@ function Invoke-ScriptGenerator {
         $null = $AstParam.Remove("Encoding")
         $ParseResults = ConvertToAst @AstParam
         [StringBuilder]$Builder = $ParseResults.Ast.Extent.Text
+        # Windows PowerShell's Set-Content has no UTF8Bom encoding, but its UTF8 encoding writes a BOM
+        if (-not $IsCoreCLR -and $Encoding -eq "UTF8Bom") {
+            $Encoding = "UTF8"
+        }
         $SetContentCmd = $ExecutionContext.InvokeCommand.GetCommand('Microsoft.PowerShell.Management\Set-Content', [System.Management.Automation.CommandTypes]::Cmdlet)
     }
     process {

Tests/Integration/Source1.Tests.ps1

@@ -359,3 +359,35 @@ Describe "Regression test for #125: SourceDirectories supports wildcards" -Tag I
         $Metadata.FunctionsToExport | Should -Be @("Get-Source", "Set-Source")
     }
 }
+
+Describe "Regression test for UTF8Bom encoding on Windows PowerShell" -Tag Integration, Regression {
+    BeforeAll {
+        # The non-ASCII string returned by Source1's Set-Source
+        $NonAscii = "sto$([char]0x35E)o$([char]0x2032)p$([char]0x12D)d"
+
+        Copy-Item $PSScriptRoot\Source1 TestDrive:\Utf8BomParameter -Recurse
+        $ParameterOutput = Build-Module TestDrive:\Utf8BomParameter -Encoding UTF8Bom -OutputDirectory "$TestDrive\Utf8BomParameterOutput" -Passthru -ErrorAction Stop
+        $ParameterModule = [IO.Path]::ChangeExtension($ParameterOutput.Path, "psm1")
+
+        # Values from build.psd1 are not checked by the Encoding parameter's ValidateSet
+        Copy-Item $PSScriptRoot\Source1 TestDrive:\Utf8BomManifest -Recurse
+        $metadata = Import-Metadata TestDrive:\Utf8BomManifest\build.psd1
+        $metadata["Encoding"] = "UTF8Bom"
+        $metadata["OutputDirectory"] = "$TestDrive\Utf8BomManifestOutput"
+        $metadata | Export-Metadata TestDrive:\Utf8BomManifest\build.psd1
+        $ManifestOutput = Build-Module TestDrive:\Utf8BomManifest -Passthru -ErrorAction Stop
+        $ManifestModule = [IO.Path]::ChangeExtension($ManifestOutput.Path, "psm1")
+    }
+
+    It "Writes a BOM and UTF-8 content when UTF8Bom is passed as a parameter" {
+        $Bytes = [IO.File]::ReadAllBytes($ParameterModule)
+        $Bytes[0..2] | Should -Be @(0xEF, 0xBB, 0xBF)
+        [IO.File]::ReadAllText($ParameterModule, [Text.Encoding]::UTF8) | Should -Match ([regex]::Escape($NonAscii))
+    }
+
+    It "Writes a BOM and UTF-8 content when UTF8Bom is set in build.psd1" {
+        $Bytes = [IO.File]::ReadAllBytes($ManifestModule)
+        $Bytes[0..2] | Should -Be @(0xEF, 0xBB, 0xBF)
+        [IO.File]::ReadAllText($ManifestModule, [Text.Encoding]::UTF8) | Should -Match ([regex]::Escape($NonAscii))
+    }
+}

Tests/Public/ConvertTo-Script.Tests.ps1

@@ -23,5 +23,12 @@ Describe "ConvertTo-Script" {
             $ScriptFileCommand = Get-Command $ScriptFile
             $ScriptFileCommand.Parameters.Keys | Sort-Object | Should -Be ($BuildModuleCommand.Parameters.Keys | Sort-Object)
         }
+
+        It "Accepts UTF8Bom encoding on every edition" {
+            Remove-Item $ScriptFile -ErrorAction Ignore
+            $null = Invoke-ScriptGenerator -Path $ModuleBuilder.Path -Generator "ConvertTo-Script" -Parameters @{ FunctionName = "Build-Module"; Encoding = "UTF8Bom" } -ErrorAction Stop
+
+            $ScriptFile | Should -Exist
+        }
     }
 }